Pool type liquid metal fast spectrum reactor using a printed circuit heat exchanger connection to the power conversion system

ABSTRACT

A printed circuit heat exchanger for use in a reactor includes a core formed from a stack of plates diffusion bonded together. The core has: a top face, a bottom face disposed opposite the top face, a first side face extending between the top face and the bottom face, and a second side face disposed opposite the first side face. The printed circuit heat exchanger includes: a plurality of primary channels defined in the core, each of the primary channels extending from a primary inlet defined in the first side face to a primary outlet defined in the second side face; and a plurality of secondary channels defined in the core, each of the secondary channels extending among at least some of the primary channels from a secondary inlet defined in the top face to a secondary outlet defined in the top face.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the priority benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 62/566,980 filed on Oct. 2,2017, and U.S. Provisional Application No. 62/568,486 filed on Oct. 5,2017, the contents of which are each herein incorporated by reference.

FIELD OF THE INVENTION

The present invention is directed to pool type liquid metal fastspectrum reactors, and more particularly to pool type liquid metal fastspectrum reactors utilizing printed circuit heat exchangers. The presentinvention also relates to printed circuit heat exchangers for use inpool type liquid metal fast spectrum reactors.

BACKGROUND OF THE INVENTION

To date, liquid metal reactor designs such as, without limitation, alead-cooled fast spectrum reactor, have proposed the use of spiral tubeor bayonet style steam generators. The size of these types of steamgenerators requires the reactor vessel that hosts them to be quite largein diameter, significantly increasing the primary coolant inventory.Furthermore, the need for an internal “hot leg” in a traditionalconfiguration also increases the height of the vessel. For a lead-cooledreactor, this significant increase in coolant inventory translates tosignificant weight that must be seismically supported to protect thenuclear safety related plant components. Also, traditional steamgenerators use a high number of relatively large diameter tubes to formthe heat transfer area. These tubes introduce the risk of a reactorcoolant system (RCS) pressurization event, which requires eithercontainment or high-volume filtering, as well as an inadvertentcriticality event resulting from the rupture of one or more of thesetubes. It is typically postulated that steam or other secondary sidefluid could be drawn into the core following a tube rupture, producing adramatic shift in moderation and neutron absorption and subsequentlyproducing a local criticality event. The magnitude of the associatedevent would be sufficient to result in significant fuel damage.Accordingly, there exists a need for improved cooling arrangements forreactors.

SUMMARY OF THE INVENTION

Embodiments of the present invention take advantage of the inherentcharacteristics of a micro channel heat exchanger such, as a printedcircuit heat exchanger (PCHE), to significantly reduce the size of apool type liquid metal cooled fast spectrum reactor. Such embodiments doso while effectively eliminating the only source of reactor coolantsystem pressurization and the primary source of an inadvertentcriticality event that is typically associated with this type ofreactor.

Embodiments of the invention involve the deployment of multiple printedcircuit heat exchangers such as to form a conduit between the dischargeplenum above the reactor core and the inlet to the primary coolantpumps. The higher temperature coolant passes through the heat exchangerradially towards an annular plenum that maintains a coolant supply tothe reactor coolant pumps.

As one aspect of the invention a printed circuit heat exchangercomprises: a core formed from a stack of plates diffusion bondedtogether, the core having: a top face, a bottom face disposed oppositethe top face, a first side face extending between the top face and thebottom face, and a second side face disposed opposite the first sideface; a plurality of primary channels defined in the core, each of theprimary channels extending from a primary inlet defined in the firstside face to a primary outlet defined in the second side face; and aplurality of secondary channels defined in the core, each of thesecondary channels extending among at least some of the primary channelsfrom a secondary inlet defined in the top face to a secondary outletdefined in the top face.

The printed circuit heat exchanger may further comprise: an inlet plenumdefining a first space therein, the first space in fluid communicationwith the secondary inlets; and an outlet plenum defining a second spacetherein, the second space in fluid communication with the secondaryoutlets.

The inlet plenum may comprise a main inlet structured to be fluidlycoupled to a supply header, and the outlet plenum may comprise a mainoutlet structured to be fluidly coupled to a return header.

The secondary channels may be semi-circular in cross-section.

As another aspect of the invention a pool type liquid metal fastspectrum reactor comprises: a vessel; a lower plenum defined in thevessel; a reactor core disposed in the vessel above the lower plenum; anupper plenum defined in the vessel above the reactor core; a number ofcoolant pump inlet plenums defined in the vessel; a number of coolantpumps, each coolant pump being structured to move a fluid from one ofthe number of coolant pump inlet plenums to the lower plenum; and anumber of printed circuit heat exchangers, each printed circuit heatexchanger disposed between the upper plenum and one of the number ofcoolant pump inlet plenums. Each printed circuit heat exchangercomprises: a core formed from a stack of plates diffusion bondedtogether, the core having: a top face, a bottom face disposed oppositethe top face, a first side face extending between the top face and thebottom face, and a second side face disposed opposite the first sideface; a plurality of primary channels defined in the core, each of theprimary channels extending from a primary inlet defined in the firstside face to a primary outlet defined in the second side face, whereineach primary inlet is in direct fluid communication with the upperplenum, and wherein each primary outlet is in direct fluid communicationwith one coolant pump inlet plenum of the number of coolant pump inletplenums; and a plurality of secondary channels defined in the core, eachof the secondary channels extending among at least some of the primarychannels from a secondary inlet defined in the top face to a secondaryoutlet defined in the top face.

The reactor may further comprise: an inlet plenum defining a first spacetherein, the first space in fluid communication with the secondaryinlets; and an outlet plenum defining a second space therein, the secondspace in fluid communication with the secondary outlets.

The vessel may house a volume of a primary coolant therein, wherein thevolume of the primary coolant has a maximum level within the vessel, andwherein the inlet plenum and the outlet plenum are disposed above themaximum level.

The vessel may comprise a top lid, and the inlet plenum and the outletplenum may be disposed above the top lid.

The inlet plenum may comprise a main inlet structured to be fluidlycoupled to a supply header, and the outlet plenum may comprise a mainoutlet structured to be fluidly coupled to a return header.

The secondary channels may be semi-circular in cross-section.

The number of printed circuit heat exchangers may comprise a pluralityof heat exchangers; the number of coolant pump inlet plenums maycomprise a plurality of coolant pump inlet plenums; the number ofcoolant pumps may comprise a plurality of coolant pumps; the pluralityof printed circuit heat exchangers and the plurality of coolant pumpsmay be arranged in pairs in an annular ring above and outboard of thereactor core.

The plurality of printed circuit heat exchangers may comprise sixprinted circuit heat exchangers, and the plurality of coolant pumps maycomprise six coolant pumps.

Each printed circuit heat exchanger may form at least a portion of apartition separating the upper plenum from a respective coolant pumpinlet plenum.

BRIEF DESCRIPTION OF THE DRAWINGS

A full understanding of the invention can be gained from the followingdescription of the preferred embodiments when read in conjunction withthe accompanying drawings in which:

FIG. 1 is a schematic isometric view of a reactor in accordance with anexample embodiment of the present invention;

FIG. 2 is a schematic plan view of the reactor of FIG. 1 shown with thereactor lid transparent so as to show details of the layout ofcomponents within the reactor vessel;

FIG. 3 is another schematic isometric view of the reactor of FIG. 1shown with the reactor lid, reactor vessel, and portions of othercomponents transparent to show details of internal components of thereactor;

FIG. 4 is a schematic sectional view of a reactor such as shown in FIG.1 with primary coolant flow depicted;

FIG. 5 is a schematic plan view of a reactor such as shown in FIG. 1with primary coolant flow depicted;

FIG. 6 is a schematic elevation view of a printed circuit heat exchangerin accordance with an example embodiment of the present inventionshowing primary coolant flow therethrough; and

FIG. 7 is a schematic view of the printed circuit heat exchanger of FIG.6 showing secondary side coolant flow therethrough.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which examples of theinvention are shown. The invention may, however, be embodied in manydifferent forms and should not be construed as limited to the examplesset forth herein. Rather, these examples are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the invention to those skilled in the art. Like numbers referto like elements throughout.

As used herein, “number” shall be used to refer to any non-zero integer,i.e., one or a quantity greater than one (i.e., a plurality).

A printed circuit heat exchanger (PCHE) is comprised of a stack ofchemically etched plates that are diffusion bonded together such thatdiscrete micro channels form for each of the process fluids betweenwhich heat is to be exchanged. Such configuration allows a relativelylarge heat transfer area to exist in a small volume. In one embodimentof the present invention, the use of a PCHE in lieu of a spiral woundtube style heat exchanger, the diameter of the reactor is reduced fromabout 11.5 meters to about 8 meters and the associated volume of coolantrequired is reduced to approximately 50% of its original volume. For alead-cooled reactor example, the total weight of the coolant would bereduced from approximately 7,500,000 kg to approximately 3,500,000 kg,subsequently reducing the cost of the seismically qualified structuresrequired to support this weight. Such reduction in coolant mass alsosimplifies the challenges associated with chemistry control andcorrosion protection.

Departing from the traditional PCHE configuration, in the presentinvention the secondary side micro channels are generally u-shaped,allowing for both of the supply and return headers for the secondaryside fluid to be attached to a single side of the PCHE. Thisconfiguration allows for the PCHE to be positioned in a pool typereactor such that the supply and return headers and the associatedpiping remain at least above the level of the primary coolant, andpreferably above the reactor lid. Given that any postulated rupture ofthe supply and return headers and supply piping would not result in theintroduction of secondary side fluid into the primary coolant, theassociated risk of a related criticality event is greatly reduced oreliminated by this arrangement. In addition, this generally eliminatesthe only pressurization source within the RCS, eliminatingpressure-holding containment requirements or large volume filteredvents.

Another modification from a traditional PCHE is the use of largerchannels for the primary flow. This “hybrid” arrangement optimizes theflow channel size and shape for each working fluid, accounting for theirheat transfer characteristics as well as desired thermo-hydraulicperformance and plugging avoidance.

A schematic isometric view of a reactor 10 in accordance with an exampleembodiment of the present invention is illustrated in FIG. 1. Reactor 10includes, and is generally defined by, an outer vessel 12, and a lid 14.Reactor 10 further includes a number of printed circuit heat exchangers(PCHEs) 16 and a number of primary coolant pumps 18, each shown in-partextending outward from lid 14. In the example embodiment describedherein, an arrangement of six PCHEs 16 (PCHEs) and six primary coolantpumps 18 are utilized. As shown in FIG. 2, the PCHEs 16 and coolantpumps 18 are arranged in pairs in an annular ring outboard of a reactorcore 20. Also, in the illustrated example embodiment, each pump 18 ispaired to a PCHE 16. Such pairing is achieved through the use of radialbaffles 22 that create a flow path that is unique to each pair. Theincorporation of a unique flow path allows for single or multiplePCHE(s) 16 and corresponding pumps 18 to be removed from service whilecontinuing with plant operation. The operator may choose to remove aPCHE 16 from service for maintenance/service or to adjust power outputlevel for load following maneuvers. It is to be appreciated thatnumerous alternate quantities and/or arrangements of pumps 18 and PCHEs16 can be utilized without varying from the scope of the presentinvention.

FIGS. 1-3 provide schematic illustrations of the reactor 10 and reactorinternals layout for one example embodiment of the invention. In thesefigures, the support structures for the coolant pumps 18 and the PCHEs16 are depicted as transparent to allow for a better understanding ofthe physical characteristics of the equipment and its position withinthe reactor vessel 12. FIG. 2, a plan view of the reactor 10, bestillustrates the hexagonal shape of the reactor core 20. In thisdepiction, the reactor core 20 is assumed to be comprised of multiplehexagonal fuel and neutron reflector elements, such that the overallshape of the reactor core 20 itself is hexagonal. This is one of manypossible arrangements that can be proposed for a fast reactor. In thiscase, the arrangement of six pairs of pumps 18 and PCHEs 16 works wellwith the assumed hexagonal shape of the reactor core 20.

FIG. 2 also best illustrates the radial baffles 22 that form theseparate flow paths for each pump 18 and PCHE 16 pair. The radialbaffles 22 can be seen separating each pair of PCHEs 16 and each pair ofcoolant pumps 18.

FIG. 3 provides an isometric view of the components that are housedwithin the reactor 10 and supported by the reactor internal structures(shown as transparent). In the illustrated example embodiment, each pump16 is presumed to be a propeller style axial pump that uses acylindrical baffle 24 that is integral to reactor internals supportstructure 26. This pump style allows the electric motor 28 of each pump16 to be located above the free surface of the reactor coolant and inthis case above the 12, and thus outside of the reactor 10 itself, thusremoved from the high temperature environment. It is to be appreciatedthat other pump arrangements may be utilized without varying from thescope of the present invention.

FIG. 4 shows an elevation schematic of preferred embodiment of theinvention. In this figure, solid (heated coolant) and dashed (cooledcoolant) arrows are used to depict the flow of primary and secondarycoolant and its relative temperature. Designating primary coolantdischarging from the reactor core 20 as having a temperature T_(hot) andprimary coolant discharging from the PCHE 16 as T_(cold), the primarycircuit of the reactor can be described as follows. Primary coolantenters the primary coolant pumps 18 at T_(cold). The primary coolant Pis pressurized by the pump 18 as it enters the reactors lower plenum 30.The coolant then passes through the channels of the fuel assemblies andis heated to T_(hot) by the nuclear fission reaction in the reactor core20 and discharged to the upper plenum 32. From the upper plenum 32, theprimary coolant is allowed to flow radially (i.e., outward fromlongitudinal axis 34 of FIG. 4) through the micro channels of the PCHE16 back into reactor coolant pump inlet plenum 36. While passing throughthe PCHE 16, the primary coolant P transfers its heat to the secondaryside fluid S and in doing so is returned to T_(cold). From such heattransfer, the secondary side fluid S is heated and then used in thepower conversion system (not illustrated) to produce electricity througha turbine generator set.

FIG. 5 provides a two-dimensional schematic top view of the reactor 10.This view shows one possible arrangement where the six PCHEs 16 areconnected to a single supply header 40 and a single return header 42(disposed directly below supply header 40). It also shows the primarycoolant P flow paths from the plan view perspective, using solid (heatedcoolant) and dashed (cooled coolant) arrows to indicate the relativetemperature.

In the example illustrated embodiment, PCHE supply and return headers40,42 are located outside of the reactor 10 well above the free surface44 of the primary coolant P (it is also to be appreciated thatembodiments of the present invention allow for the supply and returnheaders to be positioned outside of the primary nuclear containment aswell). In this arrangement, a postulated rupture of either the supply orreturn header or the supply and return piping for an individual PCHE 16would not pressurize the reactor 10 or introduce secondary side fluid Sinto the primary coolant P. Only the micro channels 46 (FIG. 7) of thePCHE 10 are submerged below the free surface 44 in the primary coolantP, thereby significantly reducing the risk of an inadvertent criticalityevent from a postulated rupture of the secondary side system.

Referring again to FIG. 4, the anticipated relative free surface level44 for the primary coolant P are shown. When operating, the primarycoolant pumps 18 will raise the free surface level 44 of the primarycoolant P in the core discharge plenum 32 providing the driving headnecessary to push the primary coolant P through the primary side microchannels 48 (FIG. 6) of the PCHE 16.

FIGS. 6 and 7 illustrate a schematic elevation view of a PCHE 16 inaccordance with an example embodiment of the present invention showing aschematic representation of the flow of primary coolant P therethrough(FIG. 6) and a schematic representation of the flow of secondary fluid Stherethrough (FIG. 7). PCHE 16 includes a core 50 formed from a stack ofplates diffusion bonded together. The core 50 includes: a top face 52, abottom face 54 disposed opposite top face 52, a first side face 56extending between the top face 52 and the bottom face 54, and a secondside face 58 disposed opposite the first side face 56.

Referring to FIG. 6, PCHE 16 further includes a plurality of primarychannels 48 (five are shown in FIG. 6) defined in the core 50. Each ofthe primary channels 48 extend from a primary inlet 62 defined in thefirst side face 56 to a primary outlet 64 defined in the second sideface 58. Each of primary channels 48 may take on many different shapesor forms without varying from the scope of the present invention. Forexample, primary channels may be formed by machining, plate forming, orany other suitable process without varying from the scope of the presentinvention.

Referring to FIG. 7, PCHE 16 further includes a plurality of secondarychannels 46 (only one is shown in the illustrated example) defined inthe core 50, each of the secondary channels 46 extends among at leastsome of the primary channels 48 from a secondary inlet 72 defined in thetop face 52 of core 50 to a secondary outlet 74 defined in the top face52 of core 50. Each of secondary channels 46 may be formed via anetching process. Accordingly, secondary channels 46 typically have asemi-circular, circular, or oval cross-section. However, it is to beappreciated that secondary channels 46 may have other cross-sectionalshapes without varying from the scope of the present invention.

As shown in both FIGS. 6 and 7, PCHE 16 further includes an inlet plenum80 which defines a first space 82 therein which is in fluidcommunication with the secondary inlets 72; and an outlet plenum 84which defines a second space 86 therein which is in fluid communicationwith the secondary outlets 74. The inlet plenum 80 includes a main inlet90 which is structured to be fluidly coupled to a supply header, and theoutlet plenum 84 includes a main outlet 92 which is structured to befluidly coupled to a return header.

Although shown as being generally straight or U-shaped, it is to beappreciated that the shape of primary channels 48 and secondary channels46 may vary without varying from the scope of the present invention. Italso to be appreciated primary channels 48 and secondary channels 46 maybe arranged generally according to various flow patterns, e.g., withoutlimitation, cocurrent, countercurrent, cross-current, or combinationsthereof, without varying from the scope of the present invention.

From the foregoing examples it is to be appreciated that the arrangementwithin the reactor results in a compact design that reduces the size ofthe reactor, the required inventory of coolant and the associatedreduction in weight and chemistry control difficulty associated withboth. The micro channels used on the secondary side of each PCHEeliminates the risk of a criticality event resulting from a pipe rupturetypically associated with traditional steam generators. The microchannels used on the secondary side of the PCHE eliminates the risk of alarge pressurization source within the RCS, eliminating the need forhigh-pressure containment or large-volume filtering. The micro channelsused on the primary side of the PCHE are of a different size than thoseon the secondary side. This optimizes performance and meets the designobjectives unique to each heat transfer medium. Modifications to aconventional PCHE that facilitate the removal of the criticality riskare: introduction of u-shaped secondary side fluid micro-channels;connection of secondary side fluid supply and return plenums to a singleside; and secondary supply and return headers remain above the level ofthe primary coolant (and outside of the reactor and/or outside of theprimary nuclear containment). The arrangement allows for the deploymentof reactivity control devices such as control rods directly above thereactor core. The arrangement promotes natural circulation of theprimary coolant in the event that power is lost to the primary coolantpumps. The arrangement reduces corrosion risk to the reactor vesselsince heat added to the coolant by the reactor core is removed before itmakes contact with the shell of the reactor vessel. The arrangementreduces corrosion risk to the reactor coolant pump impeller as theprimary coolant temperature is reduced by the PCHE before it enters theprimary coolant pump plenum. The extended length of the plenum area addsmass above the free surface which offsets buoyancy of the PCHE in lead.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangements disclosed are meant to be illustrative only andnot limiting as to the scope of invention which is to be given the fullbreadth of the claims appended and any and all equivalents thereof.

What is claimed is:
 1. A pool type liquid metal fast spectrum reactorcomprising: a vessel comprising a top lid, wherein the vessel houses avolume of a primary coolant therein, and wherein the volume of theprimary coolant has a maximum level within the vessel; a lower plenumdefined in the vessel; a reactor core disposed in the vessel above thelower plenum; an upper plenum defined in the vessel above the reactorcore; a number of coolant pump inlet plenums defined in the vessel; anumber of coolant pumps, each coolant pump being structured to move afluid from one of the number of coolant pump inlet plenums to the lowerplenum; and a number of printed circuit heat exchangers partiallysubmerged below the maximum level of the primary coolant, each printedcircuit heat exchanger disposed between the upper plenum and one of thenumber of coolant pump inlet plenums, each printed circuit heatexchanger comprising: a core formed from a stack of plates diffusionbonded together, the core having: a top face, a bottom face disposedopposite the top face, a first side face extending between the top faceand the bottom face, and a second side face disposed opposite the firstside face; a plurality of primary channels defined in the core, each ofthe primary channels extending from a primary inlet defined in the firstside face to a primary outlet defined in the second side face, whereineach primary inlet is in direct fluid communication with the upperplenum, and wherein each primary outlet is in direct fluid communicationwith one coolant pump inlet plenum of the number of coolant pump inletplenums; and a plurality of secondary channels defined in the core, eachof the secondary channels extending transversely across at least some ofthe primary channels from a secondary inlet defined in the top face to asecondary outlet defined in the top face; an inlet plenum in fluidcommunication with the secondary inlets, wherein the inlet plenumextends from the top face and through the top lid, and wherein the inletplenum comprises a main inlet configured to be fluidly coupled to asupply header at a location above the maximum level of the primarycoolant; and an outlet plenum in fluid communication with the secondaryoutlets, wherein the outlet plenum extends from the top face and throughthe top lid, and wherein the outlet plenum comprises a main outletconfigured to be fluidly coupled to a return header at a location abovethe maximum level of the primary coolant.
 2. The pool type liquid metalfast spectrum reactor of claim 1, wherein: the inlet plenum defines afirst space therein, the first space in fluid communication with thesecondary inlets; and the outlet plenum defines a second space therein,the second space in fluid communication with the secondary outlets. 3.The pool type liquid metal fast spectrum reactor of claim 1, wherein theinlet plenum and the outlet plenum are disposed above the maximum level.4. The pool type liquid metal fast spectrum reactor of claim 1, whereinthe inlet plenum and the outlet plenum are disposed above the top lid.5. The pool type liquid metal fast spectrum reactor of claim 1, whereinthe secondary channels are semi-circular in cross-section.
 6. The pooltype liquid metal fast spectrum reactor of claim 1, wherein the numberof printed circuit heat exchangers comprises a plurality of printedcircuit heat exchangers; wherein the number of coolant pump inletplenums comprises a plurality of coolant pump inlet plenums; wherein thenumber of coolant pumps comprises a plurality of coolant pumps; andwherein the plurality of printed circuit heat exchangers and theplurality of coolant pumps are arranged in pairs in an annular ringabove and outboard of the reactor core.
 7. The pool type liquid metalfast spectrum reactor of claim 1, wherein the number of printed circuitheat exchangers comprises six printed circuit heat exchangers, andwherein the number of coolant pumps comprises six coolant pumps.
 8. Thepool type liquid metal fast spectrum reactor of claim 1, wherein eachprinted circuit heat exchanger forms at least a portion of a partitionseparating the upper plenum from a respective coolant pump inlet plenum.